Fix use of old PromQL parser in rules lint (#55)

In #49, I introduced a bug that referenced the old PromQL parser. The
legacy one is not compatible with the current one and thus fails to
parse any of our current rules files.

Author: gotjosh

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## unreleased / master
 
+* [BUGFIX] Fix usage of the old PromQL parser in `prepare lint`.
+
 ## v0.2.1 / 2020-06-08
 
 * [FEATURE] Add `rules check` command. It runs various [best practice](https://prometheus.io/docs/practices/rules/) checks against rules.

pkg/rules/rules.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"strings"
 
-	promql "github.com/cortexproject/cortex/pkg/configs/legacy_promql"
 	rulefmt "github.com/cortexproject/cortex/pkg/ruler/legacy_rulefmt"
 	"github.com/prometheus/prometheus/promql/parser"
 	log "github.com/sirupsen/logrus"
@@ -30,7 +29,7 @@ func (r RuleNamespace) LintPromQLExpressions() (int, int, error) {
 	for i, group := range r.Groups {
 		for j, rule := range group.Rules {
 			log.WithFields(log.Fields{"rule": getRuleName(rule)}).Debugf("linting PromQL")
-			exp, err := promql.ParseExpr(rule.Expr)
+			exp, err := parser.ParseExpr(rule.Expr)
 			if err != nil {
 				return count, mod, err
 			}

pkg/rules/rules_test.go

@@ -137,12 +137,19 @@ func TestLintPromQLExpressions(t *testing.T) {
 			count:    1, modified: 0,
 			err: "",
 		},
+		{
+			name:     "with a complex expression",
+			expr:     `sum by(cluster, namespace) (sum_over_time((rate(loki_distributor_bytes_received_total{job=~".*/distributor"}[1m]) * 60)[1h:1m])) / 1e+09 / 5 * 1 > (sum by(cluster, namespace) (memcached_limit_bytes{job=~".+/memcached"}) / 1e+09)`,
+			expected: `sum by(cluster, namespace) (sum_over_time((rate(loki_distributor_bytes_received_total{job=~".*/distributor"}[1m]) * 60)[1h:1m])) / 1e+09 / 5 * 1 > (sum by(cluster, namespace) (memcached_limit_bytes{job=~".+/memcached"}) / 1e+09)`,
+			count:    1, modified: 0,
+			err: "",
+		},
 		{
 			name:     "with an invalid expression",
 			expr:     "it fails",
 			expected: "it fails",
 			count:    0, modified: 0,
-			err: "parse error at char 4: could not parse remaining input \"fails\"...",
+			err: "1:4: parse error: unexpected identifier \"fails\"",
 		},
 	}